Generally, through-silicon vias (TSVs) have been used to form electrical connections within System-in-Package (SiP) architectures to connect multiple semiconductor dies through the semiconductor die substrates. One method of forming these TSVs is known as a via-first method, in which the TSV is formed through the substrate prior to the formation of the semiconductor die's metallization layers, and the TSV is electrically connected to a metallization layer close to the substrate. However, while maintaining a low resistance path for connections to the active devices located on the substrate, such a connection actually increases the resistance of any feedthrough connections (e.g., for supplying power to another die), which must also include the resistance of the metallization layers through which the electricity must pass to get to the other side of the die.
To reduce this feedthrough resistance, another approach known as a via-last method may be used. In this method the metallization layers are formed over the substrate first, and the TSV is formed to extend through both the substrate and the metallization layers. This approach allows for a straight path through the die without the added resistance from the metallization layers. However, while reducing the resistance from one side of the die to the other side (and to other dies), such a TSV also increases the resistance to the active devices on the die in which it is located, as any electrical signal would have to travel all the way through the semiconductor die along the via-last TSV and then, additionally, travel back through the metallization layers in order to reach the active devices.
Therefore, what is needed is a system that can reduce the feedthrough resistance without increasing the resistance for connections to the active devices.